| Volatile organic compound(VOC) is one of the most harmful substances in paper-based packaging materials. The assessment of the migration of VOC from paper-based packaging to food stuffs is a key issue concerning the chemical safety of paper-based food packaging materials. Mathematical model prediction is an important tool to address this problem, in which the determination of model parameters(initial content, diffusion coefficient, and partition coefficient) is a key procedure for model calculation. Traditional methods for determining these parameters mostly based on some custom-designed device were not only labor and time consuming, but also difficult in results comparison among labs and method standardization. Headspace analysis technique based on commercial automatic headspace sampler is a useful tool to simulate and analyze VOC involved processes, such as diffusion, partition, and adsorption. Since the happening of process and the measurement of the analyte of interest can be accomplished in an in-situ and continuous way using headspace analysis, the accuracy of the determined parameters are more reliable, and the method standardization are easier. Therefore, the development of methods based on headspace analysis for the determination the characteristic parameters of VOC migration from paper-based packaging materials to food stuffs and the applications of these methods in the model evaluation will be of special interest in improving the reliability and efficiency of the assessment of the chemical safety of paper-based packaging materials.The methodologies for determining the diffusion, partition, adsorption coefficient of VOC in various media based on headspace analysis were developed, which including the determination of partition coefficient of VOC between various phases(vapor-liquid, vapor-solid, liquid-liquid, liquid-solid) based on phase ratio variation(PRV) and multiple headspace extraction(MHE) method, the determination of the diffusion coefficient of VOC in solid and liquid phase based on MHE and non-linear fitting(NLF) method, and the determination of adsorption parameters of VOC adsorbed on solid surface based on PRV and NLF method. These methodologies have extended the application of headspace analysis in phase equilibrium process studies.A novel method for simultaneously determining the diffusion and solid-air partition coefficient of methanol in paper materials using headspace GC was developed. PRV, NLF, and linear fitting(LF) methods were respectively used in the determination of diffusion and partition coefficient contained in an established model describing the diffusion and partition behavior of VOC in paper-based packaging materials in closed system. In the present method, a solvent-assisted vapor absorption technique was used to accelerate and extend the mass transfer process, which is good to the method efficiency and accuracy.A novel method for the determination of diffusion coefficient of methanol in liquid food simulant(i.e., water and olive oil) based on headspace analysis was developed. Using the MHE mode of headspace sampler, the diffusion behavior of methanol in food simulant can be monitored. Coupled with a theoretical model describing the diffusion behavior, the diffusion coefficient of methanol in food simulant can be determined. The present method is simple and reliable, suitable for method standardization.Novel methods for the determination of methanol content in paper materials, methanol and ethanol content in aqueous food, methanol content in oily food, and total acidity of aqueous food were developed based on headspace analysis. Using alkali extraction and headspace analysis, the methanol content in paper materials was determined, in which the solid-liquid equilibrium in alkali extraction and vapor-liquid equilibrium in headspace analysis were used in the calculation of methanol content. The determination of methanol and ethanol content in aqueous and oily food was based on full evaporation headspace analysis, in which the full evaporation of methanol in oily food was assisted by solvent absorption. Based on acid-base neutralization reaction between bicarbonate and the acid species, the total acidity of aqueous food was quantified by measuring the amount of carbon dioxide produced in the neutralization reaction using GC-TCD. The present method is simple, rapid, and suitable for bath testing of microscale sample.The mathematical models describing VOC migrating from paper-based food packaging to liquid food under various conditions were developed. The second Fick’s law was used to describing the diffusion behavior of VOC in food packaging and food. By solving the second Fick’s law under various initial and boundary conditions, the mathematical models for predicting the amount of VOC migration from paper-based food packaging to food under various conditions were established, which including the model describing VOC migrating from paper-based food packaging to air in closed and open system, the model describing VOC migrating from paper-based food packaging to liquid food under short-time contact and long-time contact, the model describing VOC migrating from paper-based food packaging to liquid food in an indirect way under closed and open system, and the model for predicting the total amount of VOC migrating from paper-based food packaging to liquid food in closed and open system. The predicting results showed that when 80 m L of liquid food was packaged by a paper-based food packaging with initial methanol content of 200 mg/L and thickness of 0.032 cm, in which the contact and non-contact areas were 75 cm2 and 25 cm2, respectively, and the void volume(gas phase) was 20 m L, the methanol concentrations in liquid food due to migrating at 60 oC for 7 h in closed and open system were 2 mg/L and 1.75 mg/L, respectively. Under these conditions, the equilibrium concentrations of methanol in liquid food, i.e., migrating at 60 oC for infinite time, were 4 mg/L and 3.5 mg/L for closed and open system, respectively.The mathematical models for predicting methanol formation in chemical pulp production were developed. Based on chemical reaction kinetics, a novel model for predicting the methanol formation during kraft pulping process was established, in which the dynamic change of alkali concentration was taking into consideration, and a kinetic model for predicting methanol formation in the oxygen delignification process was also developed. The results showed that the shortening cooking time followed by extended oxygen delignification will reduce the methanol formation per unit mass removal of lignin.The influences of pulp washing and paper sheet coating on methanol removal and migration were investigated. The results showed that methanol can dissolve out with the dilution of the pulp contained solution during pulp washing, and there exists solid-liquid partition equilibrium of methanol between pulp fibers and washing water, i.e., the dissolving out of methanol in single washing exists threshold. The influence of coating on diffusion coefficient was not significant, while the opposite result was found on partition coefficient. Thus, as to the VOC emission process determined by diffusion rate other than desorption rate, the influence of coating on it was not significant. |
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